Aircraft nose-wheel or tail-wheel mounting



Feb, 27, .1951 G. H. DOWTY 2,543,233

AIRCRAFT NOSE-WHEEL OR TAIL-WHEEL MOUNTING Filed Aug. 22, 1949 5 SheetsSheet l Inventor 62 0a 1: /7 Don/r);

v yWfM A from eys Feb. 27, W51 G. H. DOW-TY 2,543,233

AIRCRAFT NOSE-WHEEL OR TAIL-WHEEL MOUNTING Filed Aug. 22, 1949 5 Sheets-Sheet 2 1 Inventor @0665 Do PVT y Attorneys Febo 27 1951 ow-w 2,543,233

AIRCRAFT NQSE-WHEEL OR TAIL-WHEEL'MOUNTING Filed Aug. 22, 1949 5 Sheets-Sheet 5 lnvemar GfqQG f/, Don TY,

Aom eys G. H. DOWTY AIRCRAFT NOSE-WHEEL OR TAIL-WHEEL MOUNTING Filed Aug. 22, 1,949

5 Sheets-Sheet 4 Feb, 27, 31951 G. H. DOWTY AIRCRAFT NOSE-WHEEL 0R TAIL-WHEEL MOUNTING Filed 22, 1949 5 Sheets-Sheet 5 w m ma m W m e m Patented Feb. 27, 1951 AIRCRAFT NGSE-WHEEL R TA IL WH-EEL MOUNTING George H. Dowty, Chelten'ham, England Application August 22, 1949, Serial No. 111,645 In Great Britain February 24,, .1948

12 Claims.

This invention relates to aircraft nosewheel or tail-Wheel mountings which are arranged to be castorable through 369 degrees, and seeks to provide an improved and simplified construction including means for damping shimmy or for both damping shimmy and eiiecting steering. The mountings may be retractable or fixed and will usually have provision for affording self-alignment in a fore and aft or other track.

According to one feature of this invention, an aircraft castorable and steerable nose-wheel or tail-wheel mounting comprises a single doubleactin hydraulic jack the movable element of which is drivingly connected to the upper end of the rotatable part of the mounting eccentrically of the castoring and steering so that axial displacement of said element with respect to the fixed element effected by fluid in the fluid pressure system is translated into part rotary steering movements of the mounting part, whilst the fluid pressure system includes a by-pass permitting castoring of the wheel to take place independently of steering.

The by-pass perferably includes a restriction, which may with advantage be adjustable, whereby a certain amount of restraint is afforded to the castoring action. Although such a restricted by-pass may be effective at all times, that is to say when the aircraft is grounded, it may be normally effective and rendered ineffective, as by valve means, wherever steering is taking place.

According to another feature of the invention, an aircraft castorable nose-wheel or tail-wheel mounting comprises a single double-acting hydraulic jack device the movable element of which is drivingly connected to the upper end of the rotatable part of the mounting eccentrically of the castoring axis so that castoring of said rotatable part will be translated into axial displacement of the movable element of the jack device, and the hydraulic system includes a restricted .by-pass whereby the jack device functions as a dashpot to damp shimmy.

From the point of view of shimmy damping the restriction of the restricted by-pass vmay be formed in the piston member of the jack plunger. Where provision is made for steering it is also possible for the restricted by-pass to be effective at all times in which case the restriction may likewise be formed in the piston member of the jack plunger.

In order that the invention may be more clearly understood and readily carried into efiect, some embodiments will now be described by way of example with reference to the accompanying drawings; of which:

Figures 1 to 6 illustrate :an aircraft castorable rod 21.

and steerable nose-wheel mounting, Figures 1 and 2 being side and rear elevations respectively of the complete mounting, Figure 3 being a sectional side elevation of, the upper part of the mounting drawn to an enlarged scale, Figure t being a sectional view on the line IVIV in Figure 3, Figure 5 being a plan view looking down on Figure 3, and Figure 6 being a schematic diagram illustrating the hydraulic system of the mounting;

Figure '7 is a plan view of a modification and Figure 8 is a plan view of a further modification.

In the nose-wheel mounting shown in Figures 1 to .6, twin wheels H are journalled on a lever 52 which is pivoted .at [3 to the lower end of a bracket lil which is rigid with a rotatable shaft or column 15 borne in a non-rotatable support or casing 15. The casing 15 is supported near its upper end in trunnion bearings ll about which the mounting is retractable by retracting mechanism indicated generally at A8. The upper end of the casing 16 mounts .a double-acting hydraulic jack device 19., .a control and followup valve mechanism 2%, and self-centering means 21. A shock absorber .22 is arranged between the lever 12 and bracket 14.

The upper end of the rotatable column 15 (see Figure 3) is in splined connection at 23 with an extension fitting 24 which has an upstanding eccentric pin 25, through which the steering and castoring control over the column i5 is effected. The non-rotatable casing 'l 6 has a pair of integral arms 25 between which there extends a fixed hollow rod 21' formed centrally thereof with a piston 28 (see particularly Figure 4). The piston 28 has two restrictions or openings 29 and 39 extendingtherethrough, the restriction 29 communicating with the hollow 3| in rod 2? at the one side of the piston 28 and the restriction 3 communicating with the corresponding hollow '32 at the other side of the piston. The arms 25 have unions 33 for connection with the hydraulic system and through which communication is had with the hollow spaces 3! and 32.

The cylinder 3 fits slidably around the piston 28 and is glanded at its ends for sliding on the ihere is integral with the cylinder 3! a pair of lugs 35 between which are pivoted about a pin 36 one end of a link 3? the other end of which link is pivoted around the upstanding pin 25 at the top of the column 45.. It will be seen that as the cylinder 34 is caused to slide along the piston rod Z'l, the linear movement of the oyl inder will impart turning movements to the column l5 through the link 31.

The uppermost lug of the pair of lugs 35 carries a roller which co-operates with a forked arm 39 of the control and IOhOW-UP valve mechanism it. The mechanism 2c is of a known kind, and its function will be hereinafter described with reference to Figure 6.

The cylinder ti l has a downward extension ll] of cylindrical form which is adapted to slide on a pair of spring housings ll and aitcontaining a spring 43 extending between the arms 25 of the casing it. The housings Ill and a2 have shoulders i l and respectively engaging shoulders at and at respectively of the extension 4%. As the cylinder 34 moves, say to the left as seen in Figure i, it will slide over the housing H and carry with it the housing 42 in order to compress the spring 43 which acts to return the cylinder t l to its mid position along the rod 21. similarly when the cylinder moves to the right it compresses the spring 53 by carrying the housing cl with it. The spring 43 is thus a centering spring which serves to return the wheels ll into the desired alignment.

The operation of the mechanism described will be understood from the following description given in conjunction with the diagrammatic representation in Figure 6. The hydraulic system is controlled by a main stop valve unit at including a pilot valve as controlled electromagnetically through a valve positioning arm ba. The electrical circuit includes microswitches 56, i, and 52. When the electrical circuit is completed, an electro-magnet is energised to shirt the pilot valve e9 from the one extreme position shown, into which is it normany biased by suitable means (not shown), into the other extreme position. Electro-magnetically controlled valves, sometimes referred to as solenoid valves, are well known devices of which there are various suitable types already available in the art. W hen the aircraft becomes airborne, the switch 521 breaks the electrical circuit so that the pilot valve 69 will assume the position shown, closing oil duct ill, at which the hydraulic system is inoperative so far as steering is concerned. The SWitCh 5i can be caused to make or break under the control of the pilot, and the switch 52 is controlled by the angular disposition of the column i5. This latter switch 52 is shown in Figure 3 and is controlled by a cam surface co-operating with a roller It is to be noted that steering is to be effective throughout a limited range and that beyond this range the hydraulic system is to be ineffective. Thus throughout the steering range the cam surface 53 will allow the switch 52 to close, and beyond this range will break the switch and hence break the electrical circuit of the pilot valve electro-magnet. When the electrical circuit is broken and the pilot valve i9 is biased into the position shown, opposite ends of the hollow piston rod 2'2 communicate through a by-pass passage-way including conduits 55, 55, and 5?. Thus when the cylinder moves as a result of castoring rotation of the column l5, the hydraulic fluid will be able to circulate round a first by-pass passage or circuit including the restrictions 29 and 35 in the piston 28. These restrictions 29 and 36 will therefore operate as damping orifices to damp out any shimmy that may tend to develop. A second by-pass 58 between the conduits 5'! and 55 includes a two-way pressure relief valve 59 which serves to prevent excessive pressures being generated by sudden shock loads. The

first by-pass passage-way is adapted to be closed by a by-pass valve 50 but this valve remains open under the influence of its spring so long as the pilot valve t9 is in the position shown.

"When the electrical circuit is completed, as by closure of all three switches, 50, El and 52, the pilot valve 49 will move to the other extreme position and open a conduit 5| to the space '62 between a pair of piston valves 63 and 53. Pressure from the aircraft hydraulic system enters the stop valve unit at 65 and forces the piston valves and 64 apart to open their seatings. Pressure fluid can then flow from 65 along the conduits all and S5 to the end of the by-pass valve in order to shift the latter against its spring to close the section 56 of the first by-pass passage-way. The hydraulic fluid can also flow from 65 across the now open piston valve 63 and along the delivery conduit 6'! to the control valve A return conduit 69 from the control valve is now open to the reservoir across the seating of the piston valve member 64. The conduit 55 communicates with the spaces '50 and "ii of the control valve through a cross conduit 2. Unless the pilot elects to steer the mounting, the control valve closes the delivery conduit 3?. -When the pilot wishes to steer the mounting he moves the steering rod 13 to rock the arm a l of the follow-up valve in the appropriate direction. As the by-pass valve 50 has now closed the by-pass passage-way, the cylinder 34 is hydraulically locked against movement so that the roller 38, in any given position of the cylinder at, hence of the wheel support shaft l5, serves as a fixed fulcrum for the forked arm 39. The rocking of the lever i l will therefore roclr the lever 15 about the pin 16 and so shift the control valve member 11 either to the right or to the left as selected. The delivery conduit 5? will then be placed in connection either with the conduit 55 or with the conduit 51 in order to shift the cylinder 34 along the rod 21. In so moving, the roller 38 carried by the cylinder will turn the forked arm 39 which will exercise a follow-up movement by rocking the lever about the pin 18 to return the valve member ii to its original position at which connection between the delivery conduit 61 and either one conduit 55 and 51 will be cut off. Whenever delivery flow is permitted from the delivery conduit 5'! into one or other of the conduits 55 and 51, the other of the conduits 55 and 5? will communicate with the reservoir through the corresponding section of the control valve 98 and through the return conduit 59.

It is to be noted that the eccentricity of the pin 25 with respect to the castoring axis, the length of the link 3'1, and the permitted length of travel of the cylinder 34 are such that the rotatable column l5 is permitted to turn or free castor through 360 degrees. Steering is effective in a typical case for approximately 60 degrees on either side of the midposition. It will also be noted that the second by-pass passage 58 remains effective to prevent excessive pressure from shock loads during steering as well as during free-castoring of the wheel.

Referring now to the modification shown in Fig. 7, a double acting hydraulic jack device it serves merely as a shimmy damper although it will be understood that by connecting it, as'

by conduits 55 and 5'! in the form previously described, with a suitable hydraulic system it would also be used to effect steering throughout a limited range whilst permitting castoring age-races totake place throughout the remainder of theturning range. In this arrangement the casing 83: or the Jack device 6 9 is pivoted at one end about a pin 8% arranged parallel with and eccentricaliyof the axis 82 of the castorabl'e column 83. The piston 8d of the jack device T9 ismounted on a rod 85 which is pivotally con-- nected at 86 to a lever which is fulcrumed: at 88 and is connected at- 89: by alink 9&- with.

the column 83- aboutan eccentric axis 9 t. The

cylinder Sil swings to and fro transverselyaboutits pivotal attachment tothe pin 8!, which obviouslynecessitates that the above mentioned fluid connections to the opposite endsof the, i

cylinder be of a flexible type.

In the arrangement shown in Figure 8- the hydraulicjack device oscillates transversely about an end fulcrum as in Figure 7, but in this casethe piston rod is anchor d to the fulcrum and the cylinder is connected with. the castorable column. As shown in barest detail,- a double acting jack device has its piston rod 34 fulcrumed about a pin %5 on the casing or fixed part 3: of the mounting. Thec'astcrab-le column 9.7 is pivotally attached tothe' cylinder 98. of. the jack device about a pivot 83 disposed ec-' centrically of the. castoring axis. As in the pre vious arrangement, the column s": is capable of castoring through 360 degrees. The cylinder Ei8= is, however, extended to accommodate the selfoenteringspring I tit which is housed in a similar manner to the spring 53 of the Figures 1- to- 6 arrangement. That-isto say, when the cylinder is moved one direction it: carries one of the spring housings with it to: compress the spring, and when the cylinder is moved in the opposite direction it carries the other spring housing with it. The spring its always acts to return the landing wheel into a predetermined angular alignment. Again the jack device 93 may be utilised to effect steering throughout a limited range by connecting with it a suitable hydraulic system as before.

The invention thus permits castoring throughout 360 degrees yet makes provision either for shimmy damping or for both shimmy damping and steering by means of a single double-acting jack by arranging the latter at the upper end of the rotatable part of the mounting. Hitherto it has been customary when steering alone is effected by jacks to employ two jacks at diametrically opposite parts of the steering column, one jack serving to turn the mounting clockwise and the other anti-clockwise.

I claim:

1. A castorable wheel mounting, comprising a castor shaft carrying the wheel, fixed support means supporting and guiding said shaft for rotation continuously through a 360 range, crank means fixed to said shaft eccentrically thereof for rotation conjointly therewith, double-acting hydraulic jack means having a piston and coacting cylinder one of which comprises a movable element pivotally connected to said crank means, and the other of which comprises a fixed element, displacement of said movable element relative to said fixed element accompanying rotation of said castor shaft throughout such range, restricted hydraulic fluid by-pass The proportions ofthe links and lovers are" 6;; means communicating betweenopposite ends of the hydraulie jack cylinder topermit retarded displacement of said movable element effected by rotationof said castor shaft, and thereby dam-p shimmy" of such shaft and the wheel, pressurefluid conduit means connected to opposite ends of the hydraulic jack cylinder, and flow control means coacting with said conduit means tocontroldelivery and discharge or pressure-fluid through said conduit means to and from opposite ends of the hydraulic cylinder selectively to displace said movableelement thereby for steering.

2. The c'astorable wheel mounting defined inclaim 1, wherein the cylinder of the hydraulic jackmeans comprises the movable element.

3; The castorablewheel mounting defined in claim 2, wherein the hydraulic jack means in elude a piston rod pivoted at one end thereof to the fixed support means such that reciprocation of the cylinder consequent upon rotation of" the castorshaft is accompanied by transverse swinging movement of the jack means about the piston rod pivot.

4'. The castora-ble wheel mounting defined inclaim 1, wherein the cylinder comprises the movable element, and a link interconnecting such cylinder means and" the castor shaft, and means fixing the piston transversely of the axis of the castor shaft.

5'. An aircraft castorabl'e and steerable wheer mounting adapted for connection to a hydraulic fluid pressure source, comprising a castor and steering shaft carrying the wheel, fixed suppor means guiding said shaft for rotation substantially' through a 360 range, crank means fixed to said shaft eccentricallythereof for rotation conjointly' therewith, double-acting hydhaulic jack means having a piston and coating cylinder one ofwhich comprises a movable element pi'votally connected to saidcrank means, and the other of which comprises a, fixed element, said elements coacting with said crank means for displacement of said movable element relative to said fixed element accompanying rotation of said castor shaft throughout said range, hydraulic fluid by-pass means communicating between opposite ends of the hydraulic jack cylinder to permit displacement of said movable element effected by rotation of said shaft,

pressure-fluid conduit means connected to opposite ends of the hydraulic jack cylinder, and arranged for connection to the pressure source, control means coacting with said conduit means to control delivery and discharge of pressurefiuid from the pressure source through said conduit means to and from opposite ends of the hydraulic jack cylinder selectively to displace said movable element thereby for steering, and valve means in said by-pass means, operable to cut off said by-pass means, and thereby to restrain castoring of the wheel during supply of fluid pressure from such source to the hydraulic cylinder for steering.

6. The castorable and steerable wheel mounting defined in claim 5, and allow restriction in the hydraulic fluid by-pass means retarding exchange of fluid between opposite ends of the hydraulic cylinder and thereby damping any wheel shimmy that may tend to develop when the by-pass is opened.

'7. The castorable and steerable wheel mounting defined in claim 6, wherein the by-pass restriction is formed in the piston of the hydraulic jack means.

8. The castorable and steerable wheel mounting defined in claim 5, and centering spring means reacting between the hydraulic acK piston and cylinder to return the same to an initial position relative to each other corresponding to center position of the Wheel connected to the movable element through the shaft and crank means.

9. The castorable and steerable wheel mounting defined in claim wherein the hydraulic cylinder comprises the movable element and the piston is carried fixedly by the support means, and a link pivotally interconnecting the cylinder and the shaft for conjoint reciprocation and rotation thereof, respectively.

10. The aircraft castorable and steerable wheel mounting defined in claim 5, and a second bypass intelconnecting opposite ends of the hydraulic jack cylinder and by-passing the means for cutting ofi the first by-pass, and a pressure-relief valve normally closing said second by-pass but opening the same automatically in response to excessive surges of pressure therein as a result of turning shock loads on the Wheel during steering and during castoring of the wheel.

11. An aircraft castorable and steerable wheel mounting adapted for connection to a hydraulic pressure fluid source, comprising a castor and steering shaft carrying the wheel, fixed support means guiding said shaft for rotation substantially through a 360 range, double-acting hydraulic jack means having a movable element pivotally connected to said shaft eccentrically thereof for displacement of said movable element and rotation of said castor shaft conjointiy throughout said range, hydraulic fluid by-pass means communicating between opposite ends of the hydraulic jack cylinder to permit displacement of said movable element effected by rotation of said shaft, and thereby damp shimmy of such shaft and the wheel, pressure-fluid con-= duit means connected to opposite ends of the hydraulic jack cylinder and arranged for connection to the pressure source, control means coacting with said conduit means to control delivery and discharge of pressure-fluid from the pressure source through said conduit means to and from opposite ends of the hydraulic jack cylinder selectively to displace said movable element thereby for steering, means to supply and withhold pressure-fluid from the pressure source to and from said control means at will, and means, including a valve responsive to pressurefluid so supplied from such source, to cut off said by-pass means, to restrain castoring of the wheel during supply of pressure-fluid from such source to the control means for steering.

12. The aircraft castorable and steerable wheel mounting defined in claim 11, and a second bypass interconnecting opposite ends of the hydraulic jack cylinder and by-passing the valve, and a pressure-relief valve normally closing said second by-pass but opening the same automatically in response to excessive surges of pressure therein as a result of turning shock-loads on the wheel during steering and during castoring of the wheel.

GEORGE H. DOW'I'Y.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,008,094 Chester July 16, 1935 2,254,260 Arcier et al Sept. 2, 1941 2,336,567 Potter et al. Dec. 14, 1943 2,372,710 Chisholm, Jr Apr. 3, 1945 2,393,110 Kops et a1. Jan. 15, 1946 2,424,233 Greenough July 22, 1947 

